1. Field
This document relates to an stereoscopic image display device and a driving method thereof.
2. Related Art
Stereoscopic image display devices are classified into a stereoscopic technique and an autostereoscopic technique. The stereoscopic technique uses binocular parallax images which are great in the stereoscopic effect, and may have a type of using glasses and a type of not using glasses. In the type of using glasses (“glass type”), binocular parallax images are displayed on a direct view display panel or a projector by changing polarization directions or in the temporal division manner, and polarization glasses or liquid crystal shutter glasses are used to implement stereoscopic images. In the type of not using glasses (“glassless type”), the stereoscopic images are implemented by dividing optical axes of binocular parallax images, by using optical plates such as parallax barriers provided at front and rear surfaces of a display panel.
The glass type stereoscopic image display device typically displays left eye images and right eye images on a display panel in a temporal division manner. The glasses worn by a user is constituted by a left eye shutter which transmits light for left eye images and a right eye shutter which transmits light for right eye images. Thus, the user sees only the left eye images, for example, during odd frames, and sees only the right eye image during even frames, thereby obtaining a three-dimensional effect by a binocular parallax.
In a liquid crystal display to implement stereoscopic images, liquid crystal of the liquid crystal display is slow in a response speed due to characteristics such as unique viscosity and elasticity, as shown in Equations (1) and (2).
                              τ          r                ∝                              γ            ⁢                                                  ⁢                          d              2                                            Δ            ⁢                                                  ⁢            ɛ            ⁢                                                                          V                  a                  2                                -                                  V                  F                  2                                                                                                      (        1        )            
In Equation (1), Tr indicates a rising time when a voltage is applied to the liquid crystal, Va indicates an applied voltage, VF indicates Freederick transition voltage when the liquid crystal molecules starts a tilted motion, d indicates a cell gap of a liquid crystal cell, and γ indicates a rotational viscosity of the liquid crystal molecules.
                              τ          f                ∝                              γ            ⁢                                                  ⁢                          d              2                                K                                    (        2        )            
In Equation (2), τf indicates a falling time when the liquid crystal is recovered to an original position due to the elastic recovery after the liquid crystal stops being applied with a voltage, and K indicates a modulus of elasticity unique to the liquid crystal.
The shutter glasses type stereoscopic image display device display left eye images and right eye images on a display panel in the temporal division manner. For this reason, the stereoscopic image display device is required to be driven at a higher frame frequency than a frame frequency of a 2D display device so as to temporally divide the left eye images and right eye images.
In the stereoscopic image display device, when driven at the frame frequency of 120 Hz, a data voltage for a next monocular (right eye or left eye) image is charged in the liquid crystal cell in the state where a data voltage for a previous monocular (left eye or right eye) image which has already been charged therein remains. Therefore, a user may feel a 3D crosstalk where the left eye images and the right eye images overlap each other if viewing stereoscopic images through a stereoscopic image display device driven at the frame frequency of 120 Hz.
As methods for solving the 3D crosstalk, there is a method where the frame frequency is increased to 240 Hz, and a frame period during which a black grayscale voltage is written in all the liquid crystal cells is inserted between a previous monocular image frame and a next monocular image frame. In this method, voltages at the liquid crystal cells are changed to the black grayscale voltage during the black grayscale inserting frame period and then next monocular image data voltages are written in the liquid crystal cells during a next frame period, thereby reducing the 3D crosstalk. However, this method has a problem in that a high frame frequency is required and thus costs of driving circuits increase. Therefore, there is a great request for a driving method in which the stereoscopic image display device drives 3D images at the frame frequency of the 120 Hz and the 3D crosstalk is not recognized.